Product Code: 8520110 Scientists NAICS Code: 54171 Research and Development in the Physical, Engineering, and Life
Sciences

Geographic:

Geographic Scope: United States Geographic Code: 1USA United States

Accession Number:

242015837

Full Text:

Your immune system is your body's own powerful army. It puts
up an array of sophisticated defenses against threats from within and
without. Studies in the United States and abroad increasingly point to
vitamin D as perhaps one of the immune system's strongest allies
against disease.

Now, investigations by Agricultural Research Service physiologist
Charles B. Stephensen are providing new and more precise information
about the amount of this essential nutrient that we may need for optimal
health--including a healthy immune system.

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The research is timely. Millions of Americans don't get enough
vitamin D--a deficiency that some have called one of the most serious
public health issues facing the United States today.

Scientists have known since the early 20th century that our bodies
are stimulated to make vitamin D when ultraviolet rays from the sun
reach our skin. The amount of direct sunlight that we do--or
don't--receive depends on the season, the latitude at which we
live, the amount of time we spend in the sun, the pigmentation of our
skin, and even the kind of protective clothing we wear.

We also get some vitamin D from foods, including salmon and some
other fish, milk and breakfast cereals that are fortified with this
nutrient, and supplements such as multivitamin tablets.

Findings from a preliminary, and apparently first-of-its-kind,
study of 72 young adult volunteers in northern California might help
pave the way to individualized recommendations--for the future--for
vitamin D intake. The recommendations might take into account two
personal characteristics: sun exposure and skin tone.

Stephensen is research leader of the Immunity and Disease
Prevention Research Unit at the ARS Western Human Nutrition Research
Center in Davis. California. He collaborated in the investigation with
supervisory chemist Leslie R. Woodhouse, graduate student Laura M. Hall
at the center, and others.

For 7- to 8-week stints during spring, summer, fall, and winter,
volunteers provided intermittent records of what they ate and, once a
week, wore photosensitive badges from 7 a.m. to 7 p.m. to record their
exposure to the sun. Blood samples were taken three times each season so
that scientists could monitor the volunteers' vitamin D levels,
using serum 25-hydroxyvitamin D as their indicator.

From these measurements, the researchers developed a preliminary
model that first of all assumes a vitamin D intake of 200 international
units (IU)--the U.S. adult recommended daily allowance. Then, the model
predicts the additional amount a person might need, based on the
individual's sun exposure and pigmentation.

The data from volunteers--either African-American or of European
ancestry--who had relatively low amounts of sun exposure suggests that
they may need additional vitamin D to reach a target blood level of 75
nanomoles of vitamin D per liter of plasma.

Perhaps surprisingly, "low sun exposure" would be, for
example, the amount received by a person spending no more than 20
minutes a day in direct sun, wearing long pants (not shorts), a
short-sleeved (not sleeveless) top, and no hat. "That's
similar to an average office worker's exposure," Stephensen
notes.

Details are in an article published earlier this year in the
Journal of Nutrition. Stephensen cautions that some of the intakes
indicated by the experimental model exceed the level currently
considered safe. He also notes that the findings are preliminary and
that "more research, with a larger number of volunteers" is
needed to refine the predictive power of the new mathematical model.

Nutrients Support Immunity

Among the many foods thought to play an important role in keeping
the immune system healthy are mushrooms.

In the United States, white button mushrooms represent 90 percent
of the total mushrooms consumed.

The results suggest that white button mushrooms may promote immune
function by increasing production of antiviral and other proteins that
are released by cells while seeking to protect and repair tissue.

Wu and co-investigators are with the HNRCA Nutritional Immunology
Laboratory in Boston, Massachusetts. The study's cell-culture phase
showed that white button mushrooms enhanced the maturity of immune
system cells called "dendritic cells," from bone marrow.
Dendritic ceils can make T cells--important, specialized white blood
cells that can recognize foreign substances from invading pathogens and
eventually present them to other defense system cells.

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"When immune system cells are exposed to disease-causing
pathogens, such as bacteria, the body begins to increase the number and
function of immune system cells," says Meydani. "People need
an adequate supply of nutrients to produce an adequate defense against
the pathogen. The key is to prevent deficiencies that can compromise the
immune system."

The study appears in a 2008 issue of the Journal of Nutrition.

Zinc and Vitamin E Power

HNRCA researchers are also conducting observational studies in the
area of immunology. They are studying immune response in about 600
elderly residents in 33 nursing facilities in the Boston area.

Meydani and colleagues previously reported that among the facility
residents, those who consumed 200 IU of vitamin E daily for 1 year were
20 percent less likely to get upper respiratory infections, such as
colds, than those who took a placebo.

A secondary analysis of data from the same clinical trial showed a
high proportion of the residents had low serum (blood) zinc
concentrations at baseline and after I year of follow-up. All
participants had been supplemented with half of the recommended dietary
allowance of essential vitamins and minerals, including zinc, during the
trial.

The researchers found that those with normal blood zinc
concentrations were about 50 percent less likely to develop pneumonia
than those with

low concentrations. Those with normal zinc status also had fewer new
prescriptions for antibiotics, a shorter duration of pneumonia, and
fewer days of antibiotic use compared with residents who had low zinc
levels.

The study appears in a 2007 issue of the American Journal of
Clinical Nutrition.

While the study suggests that supplementation of zinc-deficient
elderly may result in reduced risk of pneumonia, the authors note that
controlled clinical trials are needed to test efficacy of zinc
supplementation as a low-cost intervention to reduce mortality due to
pneumonia among vulnerable populations who already have low zinc
levels.--By Marcia Wood and Rosalie Marion Bliss, ARS.

This research is part of Human Nutrition, an A RS national program
(#107) described at www.nps.ars.usda.gov.